Conventional retaining walls are used to secure earth embankments against sliding and slumping. Retaining walls are made of various materials such as concrete, solid masonry, wood ties, bricks and blocks of stone and concrete. Typically, blocks are placed in rows, or courses, overlaying on top of each other to form a wall. In retaining walls constructed from dry-stacked retaining blocks (i.e., walls constructed without mortar between courses), pins or rods typically are used to interconnect blocks of a lower course with vertically adjacent blocks in an overlying course. For taller walls, a horizontal tie-back sheet (commonly referred to as a geofabric or geogrid) may be located between adjacent layers of blocks, and extended rearwardly into an excavated area to be backfilled for retaining the wall against the outward force of the earth being retained. Retaining wall blocks used for relatively short walls, such as used in gardens or in landscaping applications, may be formed with integral vertical flanges or projections that engage corresponding grooves or surfaces of blocks in a vertically adjacent course to help stabilize the wall.
Another type of retaining wall system uses block assemblies having two or more interlocking subcomponents. Such a system is shown in U.S. Pat. No. 5,688,078 to Hammer. In this system, each block assembly includes a frontal or face block that is exposed in the front surface of the wall, a trunk block extending perpendicularly from the rear of the face block, and an anchor block connected to the rear end of the trunk block. The block assemblies are shaped to form spaces or voids between laterally adjacent block assemblies, which are filled with a backfill material. Additional trunk and anchor blocks can be included in each block assembly to extend the assembly deeper into the slope for adding anchoring strength. This type of wall system is advantageous in that it generally does not require the use of tie-back sheets, which require substantial earthmoving and careful filling and grading of one course at a time.
When constructing a wall, the base width of the wall (the width of the lowermost course) must extend a sufficient distance into the embankment relative to the overall wall height to resist outward movement of the embankment. The allowable height-to-width ratio of a wall depends in part on the type of retaining wall system used and the type of soil in the embankment and upon which the wall is constructed. Thus, for a specified wall height, the base width of the wall typically must be increased as the stability of the soil decreases to maintain a minimum sliding resistance. Unfortunately, increasing the base width of a wall requires additional materials and possibly additional excavation, which can be cost prohibitive. Additionally, in some cases, the embankment may not be wide enough to accommodate the placement of courses of the required width.